Spectrum is a scare resource in wireless communication systems, and is often poorly utilized. In conventional wireless networks, spectrum allocation is fixed (non-adaptive) during network planning and deployment, based on statistical characteristics of previous measured traffic. However, in practice, wireless traffic occurs in bursts, over a number of different time scales. As such, the conventional fixed allocation approach that does not adapt to traffic dynamics leads to potentially large durations when significant spectrum is underutilized, or even unused.
In existing indoor wireless networks, spectral utility (the ratio of usage to allocation) is particularly low for two reasons. Firstly, indoor deployment is traffic-oriented rather than coverage-oriented (as in outdoor networks), and a large amount of spectral resources are allocated for the expected traffic peaks. Secondly, interference cannot be coordinated due to the complicated indoor environments, and orthogonal spectrum allocation is therefore extensively employed. As a result, more spectrum and more infrastructure such as base stations are allocated than are truly necessary to handle the wireless traffic.
In conventional outdoor wireless networks, such as cellular and sensor networks, spectral utility is also relatively low. Resources such as spectrum and base stations are typically allocated to fixed, uniformly-sized cells to provide seamless coverage. However, the users' spatial distribution and consequently the spatial distribution of traffic are not uniform between cells. As such, the conventional approach of fixed cell allocation leads to an underuse of resources at some sparsely populated cells while also often failing to satisfy the traffic requests in other, heavily populated cells. This results in the inefficient utilization of spectrum, and the effective system capacity is low.